Cerebellum, balance, coordination Flashcards
what does the cerebellum do generally
it is the processing part of the brain
cortex sends info to cerebellum about what movement they want and should be happening
(coming from collateral branches from the corticospinal tract- from cerebral cortx)
cerebellum takes it on board
gets sensory info from muscle spindles, golgi tendon organs (in muscle or joint to say whether the m or tensdon has actually moved)
cerebellum alerts cortex if movement has not happened- ADJUSTMENT MOVEMENT
sends signals via rubrospinal tract from red nucleus- get changing of nucleus
signal back via thalamus to cortex and get correcting signal down corticospinal tract that brings about changing of that movement
what is the function of the muscle spindles
in muscles
give info of change of length of muslce
what is the function of golgi tendon
found in muscle
give info about tension of muscle
what are cerebellar peduncles
connect cerebellum to brain stem and cerebrum
what are the 3 types of cerebellar peduncles
inferior- connect cerebellum to medulla
middle- cerebellum to pons
superior- cerebellum to midbrain
they are input and output routes
what are the cerebellum lobes
anterior
posterior
flocculonodular lobe (base)
what are the different zones of the cerebellum
it is topographically arranged
vermis (centre)- central control
intermediate zone (limb control movement)
lateral zone
what are the functional zones of the cerebellum
- vestibulocerebellum
–flocculonodular lobe
–input from vestibular and visual areas
–output to vestibular nucleus (equilibrium and eye movements - spinocerebellum
–vermis of posterior and anterior cerebellum and intermediate zones
–input from spinocerebellar and auditory, visual, vestibular systems and sensorimotor cortex
–output from vermis to fastigial nuclei to vestibular and reticular formation of pons and medullar (antigravity muscles)
–output from intermediate zone to interposed nuclei to red nucleus to thalamus to cortex (stretch reflexes) - cerebrocerebellum
–lateral zones
–input from cerebral motor cortex
–outpit to dentate nucleus to thalamus to motor and premotor cortices
–creates feedback with cortical sensorimotor system to plan voluntary body and limb movements
what are the deep nuclei of the cerebellum
dentate– red nucleus–thalamus–cortex
interposed
fastigial
vestibular
they form the sole output from the cerebellum
what are the microscopic structure of the cerebellum
-3 major layers
molecular layer
purkinje cell layer
granule cell layer
what happens in the molecular layer
series of axons
integration of info
discuss the climbing fibers and the mossy fibers
mossy fibers synapse with the granular layer and interact with the molecular
INDIRECTLY affect purkinje cells
climbing fibers DIRECTLY affect the purkinje cells
They are both EXCITATORY
Where do the climbing fibers originate from
olive nucleus
are the purkinje cells excitatory
no they are INHIBITORY
describe what happens microscopically when there is a new movement occurring
new movement get an increase in firing– excitatory from mossy and climbing fibres
stimulate purkinje
so initial output is inhibitory
when movement is learned the inhibitory output becomes diminished
===>LONG TERM DEPRESSION
PURKINJE become PLASTIC- learning form input
what is the order of the deep cerebellar nuclei
lateral to medial (only output from cerebellar)
lateral ->medial
Dentate (lateral zones)
Interposed (intermediate)
Fastigial (vermis)
Vestibular is fed from flocculondular lobe
Dont- DENTATE
Eat- EMBOLIFORM
Greasy- GLOBOSE
Food- FASTIGIAL
what are the cerebellum functions
- acts as a comparator
(compare descending supraspinal motor signals with ascending afferent info) - acts as a timing device
(3 different kinds of cerebellum) - initiating and storing movements
(modifiable synapse- purkinje- store motor info and update it)
stimulation of cerebellum causes neither sensation nor significant movements
loss of cerebellum–> severe abnormalities of motor function
how does alcohol affect the cerebellum
affects neurons in the cerebellum
what is the primary role of cerebellum
supplement and correlate activities of other motor areas– correction of rapid muscular movement initiated by cortex (TYPING)
what is the secondary and third role of cerebellum
secondary- control of postural mechanisms
third- maintenance of tone of muscles (hyperflexia)
cerebellum informed of movement by cortex before it occurs, cereb processes sensory info to generate an ERROR SIGNAL which is fed back to cortex and movement is adjusted
what are some clinical features of cerebellar dmage
HYPOTONIA
reduced input from deep cerebellar nuclei
INCOORDINATION/ATAXIA
asynergy
dysmetria
dysdiadochokinesis
DYSARTHRIA
NYSTAGMUS
disruption between vestibular nucleus and oculomotor nuclei
PALATAL TREMOR, MYOCLONUS
rare
hypertrophy of inferior olive- damage to dentate nucleus of cerebellum and red nucleus in midbrain
what system generates our sense of balance
vestibular system
discuss the ear and
pinna collects and focuses sound waves
external auditory canal (skin lined) ends up at tympanic membrane
middle ear is air filled chamber, bounded by tympanic membrane and oval window
eustachian tube connects middle ear to nasophyarynx, allows pressure equalisation
outer, middle, inner ear
what is the membranous labyrinth
filled with endolymph
encased in temporal bone
auditory part is cochlea
what are the two vestibular parts
otolith organs* (two parts)- detect GRAVIT, HEAD TILT
semicircular canals- detect HEAD ROTATION
*saccular (vertical)
*utricle (horizontal)
what are the hair cells of saccule
mechanoreceptors that respond to minute movement changes
consists of one large KINOCILIUM and 50-150 stereocilia
cochlea–they lose their kinocilium with age
vestibular– do not lose kinocilium with age
perception of tilting/movement depends of movement of microcilia to kinocilia
discuss otolithic organs
detect changes in linear acceleration (i.e. that experienced as a car starts) and head angle
• Each hair cell synapses on an axon of vestibular nerve (part of CN VIII)
• Otoliths are particles of calcium carbonate; they are denser than the endolymph
• Otoliths are pulled by gravity and move gelatinous cap in same direction; cilia of hair cells are deflected
what is the mechanotransduction in hair cells
a 0.5 micron movement of the kinocilium open/closes hair cell cations
if cilia move towards kino
k channels open – depolarisation, increase in frequency down nerve
NT released down vestibular never
tells brain there is movement in that direction
if away close k channels and hyperpolarisation
occurs in utricles and saccules
what happens in semicircular canals (ampulla)
Sensitive to angular acceleration
• Hair cells clustered in sensory
epithelium, crista ampullaris
• Hair cells project into gelatinous
cupula, all hair cells orientated in
same direction
• As head rotates canal moves but
endolymph stays put, this bends the
hair cells and they either excite or
suppress transmitter release
depending on direction of
movement
describe the vestibular nervous pathway
Vestibular axons from CN VIII make
direct connections to vestibular
nucleus & cerebellum
• Axons from otolith organs project to
lateral vestibular nucleus, which
project via vestibulospinal tract to
spinal motor neurons – posture
• Axons from semicircular canals
project to medial vestibular nucleus,
which project via medial longitudinal
fasiculus to motor nerves of trunk
and neck muscles – keeps head
straight as body moves
how does the semicircular canals control eye movements
VESTIBULO-OCULAR REFLEX
• Direct stimulation of ampullary nerves
elicits specific eye movements
• Stimulation of afferents from left
horizontal canal causes eyes to turn
right (vestibulo-ocular reflexes)
• Specific adaption to allow gaze to
remain steady during head movement
• Lateral recti – cranial nerve VI
(abducens nucleus)
• Medial recti – cranial nerve III
(oculomotor nucleus)
describe meniere’s disease
vertigo, nausea, tinnitus, hearing loss
The vestibular apparatus is bathed in endolymph
• Normally drains to venous sinus
• Meniere’s cause is unknown, but there is an excessive accumulation of
endolymph and damage to hair cells
• Accumulation of endolymph is probably due to poor drainage
why does increased pressure in the endolymph cause both tinnitus/hearing loss and dizziness
increased endolymph in cochlear affects hearing
damage of hair cells means you dont get signals
what is vertigo
sensation of turning or rotation in space in absence of actual rotation
nausea, vomiting, gait ataxia
caused by debris from otolithic membrane adhering to cupula in ampulla of posterior semicircular canal
can be due o lesions of vestibular aspect of CNVIII or central lesions affecting brainstem vestibular nuclei.
treatment– manipulation of head, to cause calcium crystal move back to where should be
